おさらい：ラウンドマネージャー

using UnityEngine;
using TMPro;

public enum RoundState { Ready, Playing, Finished }

public class RoundManager : MonoBehaviour
{
    // シングルトン: static な Instance。Awake() で設定する
    public GameObject readyPanel;
    public GameObject playPanel;
    public GameObject finishedPanel;
    public TMP_Text roundText;
    public TMP_Text coinsText;
    public TMP_Text finalText;
    public int rounds = 3;
    public float roundTime = 4f;
    private RoundState state;
    private int round = 1;
    private int coins;
    private float timeLeft;

    void Start()
    {
        SetState(RoundState.Ready);
    }

    void Update()
    {
        // state に応じて分岐する: Ready では Space の入力を待ち、Playing では残り時間をカウントダウンする
    }

    void SetState(RoundState next)
    {
        state = next;
        readyPanel.SetActive(next == RoundState.Ready);
        playPanel.SetActive(next == RoundState.Playing);
        finishedPanel.SetActive(next == RoundState.Finished);
        if (next == RoundState.Ready) roundText.text = "Round " + round;
        if (next == RoundState.Playing) timeLeft = roundTime;
        if (next == RoundState.Finished) finalText.text = "Coins: " + coins;
    }

    // TakeCoin(): コインがカウントされるのは Playing 中だけ
}